How can I read a value from context that is provided by MultiProvider in flutter testing?

I have a component that reads from context the current (FirebaseAuth) User and checks whether it is null or not. It works in dev, however, when I want to test it with mock values, it does not.

I have mocked the auth User like so:

class MockFirebaseAuth extends Mock implements FirebaseAuth {}
var mockAuth = MockFirebaseAuth();
when(mockAuth.currentUser).thenReturn(mockUser);
when(mockAuth.authStateChanges())
    .thenAnswer((_) => Stream.fromIterable([mockUser]));

So here how the test looks:

 await tester.pumpWidget(
  MultiProvider(
    providers: [
      Provider<AuthService>(
        create: (context) => AuthService(mockAuth, mockFireInstance),
      ),
      StreamProvider<User>(
        create: (context) => context.read<AuthService>().authStateChanges,
      ),
    ],
    child: MaterialApp(
      home: SettingEmail(),
    ),
  ),
);

That is how I access the User stream from a TextFormField:

validator: (value) {
  var user = context.read<User>();
  if (user.email != currentEmailController.text) {
    return 'Email adresinizi doğru girdiğinizden emin olunuz';
  }
  return null;
},

then I get the following error:

The following NoSuchMethodError was thrown running a test:
The getter 'email' was called on null.
Receiver: null
Tried calling: email

So, how can I access that mockUser from that validator during unit test?